Technical Corner

Starter problems ?

ULPower Aero Engines are equipped with a powerful “Bendix” type starter (1) with integrated solenoid (3)  which is mounted on the op of the engine and drives the ring gear (2) at the back of the engine.

The starter solenoid is an electromagnet that activates  the coil of a contractor (a relay designed for large electrical currents – so no need to install an extra relay!) ) which then electrically connects the battery to the starter motor. The starter solenoid also moves the starter  pinion into engagement with the starter ring gear of the engine.

Let’s look at this in practical terms: A starter motor needs a large electric current (up to 135A) from the battery – more than a start button could manage without getting hot and damaged… that is why we use a starter solenoid, to keep currents in the cockpit and behind the instrument panel at lower levels, thus requiring smaller gauge wires.  When the starter button  is pressed, an  electric current is sent through the starter solenoid.  This electrical current can, especially in hot conditions, peak at about 35amps.  Although the current  only peaks for a millisecond  (a surge current), it is important to pay attention to the quality of your starter button and the use of the correct wire gauges.



If a starter solenoid receives insufficient voltage/current from the battery, it will fail to start the motor, and may produce a rapid clicking sound.

In the trouble shoot manual , which can be downloaded from, you will see that there are several things to verify before you decide to replace your starter.



Battery low:  check with new fully charged battery

Bad grounding : check that the engine is properly grounded

Bad connection +12V : Check 3AWG wire from battery to starter

Mechanical issue : with the ignition turned off, master off and key out, turn the prop by hand to find out if the crankshaft turns smoothly.



Bad contact : check that the wires are properly connected

Bad insulation: check that both connections on the starter are properly insulated to prevent short circuit

Bad grounding : check that the starter is properly grounded

Starter button: use a good quality starter button (5A min but capable of managing the 35A surge current too)

Wire size to the relay  is too small: As described in the installation manual, the wiring between the starter button and the starter solenoid, and the starter button and the 12V busbar must be at least AWG14 (use AWG 12 if the wires are long). The starter solenoid requires a lot of amps (up to 35A) , especially on a hot start, engaging the solenoid may be a problem if the wire section is too small.

If you are still  having trouble to determine the cause of your starter problem, contact your local ULP agent or service point. They will gladly help you.